A:AnswerYes, It will work. All USB mouse and Keyboards are interchangeable with any Mac computer. Including wireless/ Bluetooth USB dongles would work as well.
A:AnswerYou should try all of the slots on your dell. I had the same issue with my Dell Inspiron and ended up using a slot that I was not using any way and was not even sure that I knew I had that particuliar port.
A:AnswerNo, you would need an available USB port to use this mouse.
Although this mouse do not have the capability to connected though bluetooth doesn't mean you don't have options.
1. Not sure of your budget but you can find a nice Bluetooth mouse in the price range of ($19 to $80+) Example - Insignia™ - Bluetooth Mouse.
2. You could opt to buy a UBS extender HUB. This allows you to use more than one USB connection on one single port.
Hope this helps!